1. Field of the Invention
The present invention relates generally to weight lifting exercise machines, and is particularly concerned with an exercise arm apparatus for such a machine having pivotal linkage system for linking the arm to an exercise resistance such as a weight stack, springs, or other load.
2. Related Art
The pulldown exercise is one of the most basic and oldest exercises in fitness. It is designed to exercise the major muscles in the upper back. The earliest machines designed to perform this exercise consisted of little more than a pulley mounted on the ceiling with a rope reeved around it. The rope was attached to a load at one end and a horizontal bar at the other end. In order to perform exercises, the exerciser would sit or kneel on the ground beneath the bar, reach up and grab the bar, and pull it downward, stopping close to their head at approximately shoulder level.
In an effort to improve comfort, freestanding machines with seats attached for the exerciser were soon designed. One such machine is described in U.S. Pat. No. 3,640,528 of Proctor. The major disadvantage in these machines is that it is difficult for the user to maintain strict form when performing the exercise. The bar is attached directly to a flexible line, such as a rope, cable, belt, chain or the like, and the user can therefore pull the bar off to one side or the other, or lean backward while pulling the bar downward, which could stress or strain the muscle in the lower back. Also, this machine has a reduced range of exercise motion. The single piece horizontal bar limits the amount of exercise travel because the user cannot pull it past their upper chest or back (depending on whether it is pulled down in front or behind the head). A further disadvantage is convenience and safety. The user must tilt their head either forwards or backwards at just the right moment in order to avoid hitting themselves with the bar.
The disadvantages of the original pulldown machines brought about the development of the rigid arm pulldown machine. This consists of a frame, a seat for the user mounted on the frame, a generally U shaped exercise arm equipped with handles set apart at a distance slightly greater than shoulder width, and a resistive force or load. The arm, which is resisted by the load, is pivotally connected to the frame and angles upward in the rest position, with the handles located high above the seat. In order to perform exercises, the seated user reaches up and grabs the handles, then pulls the arm downward slightly past shoulder level. The rigid arm pulldown works the same muscles as a traditional pulldown machine. However, because it does not have a free-swinging bar extending horizontally from hand-to-hand, it provides a safer, more restricted exercise movement with a greater range of travel.
Some rigid arm pulldown machines include a four-bar linkage system as a way to control the path of travel of the exercise arm, as in U.S. Pat. No. 5,104,121 of Webb, or the resistance supplied to the exercise arm, as in U.S. Pat. No. 5,366,432 of Habing. The four-bar linkage system has four major components: a stationary member or frame, two pivoting members each pivotally connected to the stationary frame member at spaced positions, and a connecting link that is pivotally connected to the two pivoting members. One of the pivoting members acts as the exercise arm to be engaged by the user.
One disadvantage to the rigid arm design is the weight of the exercise arm. Because most of the arm is forward of the pivoting connection to the stationary frame member, it must be counter-balanced so that it will stay in the up or rest position when resistance is being removed or adjusted. This can be accomplished in several ways, such as attaching a weight to the rear end of the arm, i.e. the opposite side of the pivot to the handle, attaching springs to the rearward end of the arm to return it to the rest position, permanently pinning some weights in a stack of selectorized weights in an amount greater than the balance weight of the arm, or providing an amount of framework for the arm or arm assembly which is greater on the rearward side of the main pivot than on the handle side. Each of these options is subject to some disadvantages.
A weight attached directly to the rearward end of an exercise arm needs to increase in size and weight the closer it is placed to the pivot, or it will not offset the weight of the handle end of the arm. If the counterweight is placed close to the pivot, it will be larger and more expensive. When placed further from the pivot, the arm grows in length and the rear end travels in a large arc. This takes up more space and can pose a safety issue for anyone walking behind the machine. One example of a machine in which weight is attached to the rearward end of an exercise arm to act as a counter-balance is described in U.S. Pat. No. 5,263,914 of Simonson.
U.S. Pat. No. 5,437,589 of Habing is an example of a rigid arm pulldown machine using springs as a counter-balance to return the exercise arm to the rest position. Springs strong enough to offset the weight of the handle and allow for adequate handle travel can end up being fairly long and this will affect the design of the machine. Springs do not maintain an even resistance throughout the length of their stretch, which could affect the resistance and smoothness of motion felt by the user. Over time, springs tend to lose their tension, which would lessen their ability to counter-balance the exercise arm adequately. Additionally, springs tend to fatigue and ultimately break after repeated use, resulting in machine “down time”, additional maintenance expense, and possible injury.
In some cases, a portion of the selector weight stack is permanently pinned to provide the required counter-balance weight, for example as shown in the brochure of Magnum Fitness. One disadvantage to such a system is that the amount of resistance available to a user is reduced. This results either in less weight for the weight stack or requires a heavier weight stack, increasing the cost to manufacture the machine.
Some pulldown machines have used an increased size of framework for the arm assembly for counter-balance, as in U.S. Pat. No. 5,217,422 of Domzalski. This uses a complicated linkage system and increases both the size of the machine and the cost to produce it.